In his column “What causes ‘piss shiver’?”, “Cecil Adams” completely dismisses the most prosaic explanation of the post-micturition convulsion syndrome (PMCS) phenomenon in favor of some rather absurd speculations.
I first read this column last spring and recognized immediately that this was simply a matter of heat transfer. But instead of criticizing it immediately, I decided to wait until I had actually experienced the piss shivers again to see if it could happen when I wasn’t already cold. Several months passed with no piss shivers. Then, just yesterday, it finally happened. It had dropped down into the 50’s here and was rather chilly for the first time in many months. Just as I was finishing emptying my bladder I got the chills, complete with shivering and pyloerection (goosebumps).
It only seems to happen when you’re cold.
The process is not as simple as one might assume. The proposed mechanism by which it works is as follows:
Your body is constantly exchanging heat with the outside environment. Most of the time, heat generated through your metabolism is flowing away from your body because your body is usually at a higher temperature than the environment (heat always flows in the direction of decreasing temperature). When it’s cold out, you’re losing heat at a rapid, but relatively constant rate.
Now you start to urinate. As the urine exits your urethra, your body mass is decreasing, and the size of your thermal mass (heat capacity) is being reduced. With this reduced thermal mass, your body temperature decreases faster for the same rate of heat flux. Should your temperature dip below the threshold, the parasympathetic nervous system kicks in with the shivering in an effort to warm you back up.
If my theory is correct, we should find that piss shivers are:
More common when it’s cold. Unheated restrooms, exposed genitalia, cold/damp toilet seats, writing your name in the snow, etc. (higher heat flux).
More common with greater urinary output/more common toward the end of the urinary process (larger decrease in thermal mass).
More common in men. Men have a larger bladder capacity (larger decrease in thermal mass).
I don’t see how this follows. The heat content (in joule) of the body decreases, but the mass decreases pari passu, so the temperature should remain constant. If we are justified in making the simplifying assumptions that the energy flux is entirely the result of radiation, and that the human body is a perfect radiator, the energy flux (power per unit area) will depend only on temperature (to the fourth power), and not on heat content (according to the Stephan-Boltzmann law).
Besides, don’t women have bigger bladders than men?
Just to clarify, if there were no heat flux from your body (that is, if there were no temperature difference between you and the outside environment), the act of urinating could not lower your body temperature, assuming the urine has the same specific heat as the rest of your body (roughly 1.0 BTU/lbm-[sup]o[/sup]F). You’d be losing heat, but there’d be no change in your temperature. No change in temperature, no piss shivers.
The critical element here is the reduction in mass, and therefore heat capacity, occuring during urination, in conjunction with a constant, positive heat flux from the body, which would cause a reduction body temperature and could enable PMCS.
Good question. The column asks why we don’t experience shivers during defecation or vomiting.
The lack of shivers during vomiting doesn’t provide us with any useful information, unfortunately. It took me years to make the connection between peeing and shivers, despite having urinated several times per day. Vomiting might also cause shivers, but I can’t imagine anyone would have vomited enough times to establish causation.
Now, back to taking a crap. I don’t believe that we’ve established that taking a crap does not result in shivers. The problem with trying to observe this, which was discussed in my earlier thread entitled “No. 2, followed by No. 1. Why?”, is that defecation is often accompanied by urination, for reasons that are not obvious to me. You can imagine a person who defecates, then shivers, then urinates might assume the shivering came from the urination rather than the defecation.
Also, I believe that for most people the rate of reduction in heat capacity during defecation would be much slower than the rate of reduction experienced during urination. This might give your body more time to utilize other forms of thermoregulation, such as vasoconstriction.
I dunno about the heat capacity argument: Sure, you’re loosing mass, but how much? Let’s assume a truely heroic piss of a full liter (I doubt most folks have a bladder of this capacity, but let’s roll with it). That’s one kilogram of water… Out of what, 60 or 80 total kilograms of body mass? So this is less than 2%. Now, even when it’s a bit chilly in the house, there’s what, 25 degrees difference between body temperature and ambient? So you should shiver about as much as you would if the temperature were half a degree colder than it is. Doesn’t seem like a big effect to me.
I’ve mostly shivered outdoors and when it is cold, so the temperature difference would be much greater than 25 degrees. If I recall correctly, there has almost always been snow, or a stiff, cold, breeze present.
On the flip side, it also seems to me that a small amount of a warm beverage makes a big difference to how cold I feel. Which I would think tends to confirm this hypothesis and that even 1% of our body mass is significant.
Ok, I think you are on to something here but what you are missing is that it is the rate of change in temperature that triggers the bodies reaction. Now, lets assume a rapid rate of urination, passing the entire liter in say 5 seconds. Would a drop in ambient temperature of half a degree in 5 seconds be expected to cause one to shiver?
On the other hand, documented cases of piss shivers at temperatures above 37 C would discredit this theory more convincingly.
Except that it isn’t a sudden change. It’s not that the loss of fluid itself results in a temperature change: Immediately before urination and immediately afterwards, the body temperature would be the same. cynic’s point is that a change in body mass would have an effect on the body’s thermal regulation systems, which is true, but it would be a longer-term effect.
I find it hard to believe that this is related to temperature in any way. I grew up on the southern edge of the Sahara Desert and experienced them most of my life. Fullness of bladder prior to urination seems to make the shiver more likely to occur. Also, I’ve had them sitting down following urination during a bowel movement. My gut tells me that it’s an involuntary neurological stress relief to the full-bladder-tension being relieved - a sort of whole-body celebration and applause to that part of the body getting relief!
I’ve experienced them in a restroom at work. And I’ve not experienced them in the same restroom, which has a pretty constant temperature. So from my experience, the heat-transfer theory doesn’t hold water (heh).
On the other hand, when I was camping in the Rockies on a NOLS course, the leader told us that urinating would make you feel warmer, and she was right; I always felt a few degrees more comfortable after my morning whizz.